A 650B Randonneur for my partner Linda to satisfy her request for a road bike that is swift yet stable with a comfortable ride on gravel roads. You might also call this a Gravel Road bike. Or a Road Disc bike. 

It features 650B tyres that roll fast AND offer a smoother and less nervous ride, low-trail steering geometry that is essential for the handlebar bag. Aluminium mudguards which function better than the alternatives and a supple frame and fork that compliment the tyres.

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The frame is designed around the 650Bx42 tyres from Compass Cycle.  I chose them for their extra stability on gravel roads and low rolling resistance.  Both these traits are very noticeable compared to 700C tyres and I would recommend this wheel/tyre combination for tall riders as well.  This bike rolls equally as fast as my roadie on its 700x25C Schwalbe One Tubeless tyres, with a far smoother ride. 

The Low-Trail geometry gives stable steering with a handlebar bag loaded anywhere from zero to 3 kg of contents.  The bag and the steering are so unobtrusive and convenient that I now can’t imagine a long ride (or a short one) without it.  The rack beneath the bag is also essential to provide adequate support and control of the load. 

Why aluminium mudguards?  Because they work….  to the extent that they are not noticeable in use.  Silent.  They are even better than I expected at keeping the bike, drivetrain and rider clean and dry and are lightweight as well.

The Babyshoe Pass tyres that Compass Cycles have recently developed have been supple, fast and comfortable on real-world uneven surfaces. They are the latest development in their evidence-based efforts to develop better tyres.  To expand your knowledge of tyres and rolling resistance, you could do worse than read about some very impressive tests.  These articles aren’t the final word, but they are improving our understanding. In the hardcopy magazine-only is an explanation of the statistical analysis that underpins the tyre testing. It’s very impressive stuff. 

The aluminium mudguards by Honjo are unnoticeable in use and are silent. They kept the bike, the rider and the drivetrain very clean on a recent ride that included damp gravel roads and I’m looking forward to adding a mudflap to the front to fully realise that feature.  The stainless-steel rack from Velo-orange was modified to provide a direct mounting point for the front mudguard. I will only offer aluminium mudguards when integrated with the frame construction to suit the mudguards. On this frame, I am very pleased to say that with a great deal of attention to detail, only minimal chainstay crimping was resorted to fit the widest Honjo 650B x 61mm mudguards. Crimping tapered chainstays increases the stress in the tubing material at that point ( it adds a stress-concentration point) so it should be used as little as possible but not at the expense of frame durability. Would you be satisfied with a fishing rod that had a big crimp in it? 

I built the wheels and Velocity A23 rims are currently the best 650B road rim available.  They are also road-tubeless compatible which here give very positive tyre seating every time. 

Low-Trail geometry.  The benefit is very noticeable;  the bike can be ridden no-hands at a fast-walking pace with up to 3kg in the bag.  The same bag and load mounted to the handlebar of a “road-racing bike” produced an annoying flopping of the handlebars to one-side due to the different steering trail.  I have test-ridden a range of trail settings, having made myself an adjustable offset fork.  

The growing understanding of low-trail geometry and tyre rolling resistance being developed and shared by Jan Heine is fascinating because it is being developed and refined through double-blind testing and is not offered as the final word, but the best available knowledge and theory.  Hooray for scientific method.

The front rack was modified to attach more neatly to the fork.  The fork disc-mount runs a long way up the rear of the fork blade to distribute the load and hence minimise stress in the material. 

 

Minor features;

Stainless–steel paint-protectors are soldered to the frame beside the disc-rotors to prevent the paint being damaged by the rotors during wheel removal/installation.

The supple smaller-diameter frame tubing, longer chainstays, supple fork-blade tubing and the tyres combine to deliver a distinct comfort benefit on long rides.  If you are up to speed with the whole supple-frame, low suspension losses ‘planing’ theory that Bicycle Quarterly have been investigating then you might be interested to know that I can make you this frame from super-supple NOS 7/4/7 wall tubing)

White Industries’ beautiful new CLD hubs accept Centerlock disc rotors that give a clean look befitting a road bike.

The rear wheel has the OC (Off Centre spoking) version of the A23 rim for a more even spoke tension.

The bag is Ortlieb’s Ultimate6 Pro-M bag; it is i-Gadget ready with its transparent window in the lid.  Opening it and closing the rigid bag lid is simple and can be done even while riding and the adjustable magnetic ‘latches’ snap  the lid closed with a positive action.

The S&S travel couplers facilitate overseas air-travel.  The frame is constructed from lively Columbus’ Zona tubing and it worked out to be a 52.5cm frame size for a 5’5” 165cm tall rider.